The present invention relates generally to internal combustion engines for automotive vehicles, and more specifically, to an automotive vehicle having a starter/alternator coupled to a variable displacement engine.
Automotive vehicles with internal combustion engines are typically provided with both a starter motor and alternator. In recent years, a combined alternator and starter motor has been proposed. Such systems have a rotor mounted directly to the crankshaft of the engine and a stator sandwiched between the engine block and the bell housing of the transmission. During initial startup of the vehicle, the starter/alternator functions as a starter. While functioning as a starter, the starter/alternator provides a sufficient amount of starting torque to rotate the crankshaft of the engine before the cylinders are fired. After the engine is fired, an amount of engine torque is provided to the crankshaft from the combustion process in the cylinders. There is a finite amount of time in which both starting torque and engine torque act on the crankshaft.
Starter/alternator systems are particularly suitable for hybrid electric vehicle applications. After the engine is started, the starter/alternator is used as a generator to charge the electrical system of the vehicle.
Variable displacement engines are known to reduce energy consumption and reduce emissions. Such systems typically close off one or more cylinders at a time to reduce displacement. Reducing the number of cylinders is done when a reduced amount of power is needed. One problem associated with such systems is that the torque variation on the crankshaft may make the engine feel rough when operating, particularly at idle. Known variable displacement engines typically reduce the operating cylinders from eight to six to four. However, in certain situations an odd number of cylinders may be desirable. The torque variation in such systems would therefore be exacerbated.
It would therefore be desirable to smooth the torque in a variable displacement engine system during the various operating modes of the engine.
It is therefore one object of the invention to smooth torque on the crankshaft of the engine during operation.
In one aspect of the invention, a method of controlling the output of a crankshaft of an internal combustion engine with a plurality of cylinders having a starter/alternator coupled to the crankshaft of the engine comprises the steps of:
closing a cylinder;
monitoring crankshaft torque;
rotating the crankshaft of the engine with the starter/alternator; and
varying a torque of the starter/alternator to a predetermined torque in response to crankshaft torque.
In the preferred embodiment the predetermined torque corresponds to a torque ripple.
In a further aspect of the invention, a system has a variable displacement internal combustion engine having a crankshaft and cylinder. The crankshaft has a crankshaft torque associated therewith. The starter/alternator is coupled to the crankshaft. A controller is coupled to the starter/alternator for initiating the rotation of said crankshaft to a predetermined torque corresponding to reduce torque ripple in the crankshaft.
One advantage of the invention is that the present invention is suitable for use with variable displacement engine having high torque fluctuation.
Another advantage of the invention is that the number of cylinders may be varied and efficient operation of the engine may be maintained regardless of load.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.